(57) The continuous speed-shifting device of the present invention is provided with the first - third rotary shafts (1-3), a differential gear mechanism (5) having the first gear element (8) connected to the third rotary shaft (3), a variable speed pulley mechanism (32) which connects the first (1) and the third (3) rotary shafts speed-changeably by a belt (B), a driving power gear mechanism (20, 21) which connects the first rotary shaft (1) to the second (6) or the third (9) gear element of the differential gear mechanism (5) and a circulating power gear mechanism (22, 23) which connects the second rotary shaft (2) to the third (9) or the second (6) gear element of the differential gear mechanism (5). According to switching of the advancing and the retreating, the first rotary shaft (1) and the driving power gear mechanism (20, 21) or the second rotary shaft (2) and the circulating power gear mechanism (22, 23) are connected or disconnected by the gear clutch (35, 36). Large driving power transmitted from the first rotary shaft (1) to the differential gear mechanism (5) is passed through the gear mechanism (20, 21) but small circulating power returned to the first rotary shaft (1) from the differential gear mechanism (5) is always passed through the pulley mechanism (32). When the first rotary shaft (1) and the driving power gear mechanism (20, 21) or the second rotary shaft (2) and the circulating power gear mechanism (22, 23) are connected with each other by a gear clutch (35, 36), rotation of the third rotary shaft (3) is made zero to obtain a neutral state.